The present invention relates to a pressure-limiting valve comprising a valve housing, a valve piston with a pressure-limiting spring, wherein the pressure-limiting valve is, in particular, a pressure-limiting valve of an air treatment system for a brake system for a utility vehicle.
Air treatment systems for pneumatic brake systems, in which a safety valve for a reduced-pressure circuit for a pressure limiter is integrated, are known in connection with utility vehicles.
The air treatment arrangement is a central component in a pneumatic brake system of a utility vehicle, in which air treatment arrangement the oil- and water-containing air which is delivered by the compressor is filtered and cleaned. The compressed air is allocated, at the required pressure and in the correct filling order, to the various brake circuits and air consumers in the utility vehicle. In the event of a defect, the individual brake circuits are secured in relation to one another, so that an adequate auxiliary braking effect is available for braking the utility vehicle (for example a heavy goods vehicle). An electronic air treatment arrangement contains, in addition to a control electronics system, sensors and actuators. The most recent air treatment devices additionally also contain an electronic parking brake (EPB).
In this case, some of these brake circuits operate at a relatively low pressure level which lies below the pressure level of the other brake circuits.
In this case, the pressure can be reduced to the desired low level using a pressure-limiting valve. The desired pressure level can be adjusted by adjusting the force of the spring of the pressure limiter using an adjusting screw.
Different designs are known for pressure-limiting valves of this kind. The prior art discloses, in particular, pressure-limiting valves in accordance with the “pushing shut” principle, in which, in the event of an increase in pressure in the system, the pressure limiter closes at a defined closing pressure and thereby limits the outlet-side pressure. In the event of a further increase in pressure on the inlet side of the pressure limiter, said pressure limiter is pushed shut over an active face on the valve and the sealing force at the valve seat increases. A pressure-limiting valve of this kind is known, for example, from DE 10 2010 947 491 A1.
Further pressure-limiting valves are known from DE 33 11 816 C1, DE 26 20 135 A1, DE 41 14 977 A1, DE 30 26 283 A1, DE 26 19 769 A1, DE 26 19 769 A1, DE 600 24 496 D2 and DE 20 2006 017 517 U1, wherein these valves likewise operate in accordance with the “pushing shut” principle.
A further principle for pressure-limiting valves is the “pulling shut” principle, wherein, in the event of an increase in pressure in the system, the pressure limiter closes at a defined closing pressure and thereby limits the outlet-side pressure. In the event of a further increase in pressure on the inlet side of the pressure limiter, an active face on the piston generates a force which is introduced into the valve seat as tensile force by the piston. The sealing force at the valve seat is increased as a result.
DE 43 44 416 A1 discloses a pressure-limiting device which operates in accordance with the “pulling shut” principle. However, this pressure-limiting valve does not have a safety valve function.
Furthermore, it should be noted that the friction in a pressure-limiting valve should be as low as possible in order to keep the hysteresis of the pressure-limiting valve as low as possible. For this reason, sealing means are used in the pressure-limiting valves, said sealing means either being vulcanized-on or containing a pulled-on moulded seal. In order to safeguard the operating circuits, additional safety valves are installed. Said additional safety valves maintain the pressure in the operating circuits until the utility vehicle (for example a heavy goods vehicle) can stop. The safety valves require more installation space, and therefore more material for the valve block and more parts for assembly are required.
The object of the present invention is to advantageously develop a pressure-limiting valve of the kind outlined in the introductory part, in particular to the effect that it requires less installation space and furthermore can be manufactured at lower cost.
According to the invention, a pressure-limiting valve comprises a valve housing, a valve piston and a pressure-limiting adjusting spring, wherein at least one valve inlet and at least one valve outlet are provided in the valve housing, wherein the valve piston can assume an open position, in which the valve inlet and the valve outlet are connected to one another, and at least one closed position, in which the valve inlet and the valve outlet are separated from one another, wherein the valve piston has a first piston ring with a sealing face and has a second piston ring, wherein the first piston ring has a smaller pneumatic active surface than the second piston ring, and wherein the valve piston has, between the first piston ring and the second piston ring, a substantially truncated cone-like section which tapers in the direction of the first piston ring, wherein, in the closed position, the sealing face of the first piston ring is pulled in a sealing manner against a housing lip by a pneumatic force which acts on the first piston ring and second piston ring and which is directed against the force of the pressure-limiting adjusting spring, and wherein, furthermore, there is a pneumatic passage in the valve piston for the purpose of creating a safety valve function, which pneumatic passage can be closed by a spring-loaded safety valve body.
The invention is based on the basic idea that a safety valve is integrated in the pressure-limiting valve itself, so that an integrated safety valve function by the pressure-limiting valve is made possible. Furthermore, a pressure-limiting valve according to the “pulling shut” principle is selected since said pressure-limiting valve, in the event of the limit pressure at which the pressure-limiting valve should close being exceeded, pulls shut the valve piston and at the same time acts in a self-reinforcing manner. If a safety-critical pressure, which can likewise be pre-specified, is then further exceeded, said pressure, which triggers the safety valve function, can be reduced by the safety valve function. Owing to the integration of the safety valve function in the pressure-limiting valve itself, the installation space of the pressure-limiting valve is shared, and therefore separate installation space is not required for the safety valve. Furthermore, fewer parts are required since, owing to the integration of the safety valve in the pressure-limiting valve, a separate housing is no longer required for the safety valve for example.
Furthermore, it can be provided that the pressure-limiting adjusting spring is set on that side of the second piston ring which is averted from the first piston ring lying second piston ring. A particularly expedient introduction of the spring force, which is generated by the pressure-limiting adjusting spring, into the valve piston is achieved in this way. Furthermore, the lip which is formed by the second piston ring in any case can advantageously be used in order to mount the pressure-limiting adjusting spring on the valve piston. In this context, the body of the valve piston advantageously forms a kind of guide for the pressure-limiting adjusting spring.
Furthermore, it can be provided that only a portion of the radial face of the first piston ring is guided in the valve housing. The friction of the first piston ring in the valve housing can be reduced in this way. Furthermore, it is possible that the opening in the direction of the valve outlet, which opening is to be sealed off between the first piston ring and the valve housing, is restricted only to the gap between the first piston ring and the valve housing in the closed position.
Furthermore, it can be provided that the sealing face of the first piston ring is arranged in the radial face of the first piston ring. Simple and reliable sealing is made possible in this way. At the same time, this has the effect that the force which is required in order to lift away the first piston ring from the valve housing is comparatively low. It is also conceivable, for example, that, in the closed position, the sealing face of the first piston ring rests on an outer face of the valve housing.
It can also be provided that the sealing face of the first piston ring is formed by an O-ring and/or by a vulcanized-on sealing element. A simple and reliable sealing option is achieved in this way. Specifically, O-rings have the advantage that they can be readily exchanged. However, vulcanized-on sealing elements have the advantage that they can be fitted in a cost-effective and simple manner. However, both variants are comparatively simple and cost-effective to realize overall.
Furthermore, it can be provided that the second piston ring has a radial face which is guided in the valve housing, wherein a sealing ring is provided in the radial face. In this way, it is possible to be able to seal off the annular space, which is connected to the inlet and outlet of the pressure-limiting valve, to the outside in a simple manner in the interior of the valve housing.
The sealing ring can be formed by an O-ring and/or by a vulcanized-on sealing element.
Furthermore, it can be provided that the safety valve body is spring-loaded by the pressure-limiting adjusting spring. In this way, it is possible to be able to dispense with a separate spring for the safety valve body for the purpose of creating the safety valve function. The pressure-limiting adjusting spring can be used to adjust the pressure starting from which the safety valve body opens, in order to make the safety valve function possible.
In particular, it can be provided that the safety valve body, in a closed position, bears in a sealing manner against the sealing ring of the second piston ring. This embodiment has the advantage that it is of particularly small construction since the safety valve body bears directly against the second piston ring or is arranged in the immediate physical vicinity of the second piston ring.
The safety valve body can be guided in the valve housing. In this way, it is possible to define a defined relative movement of the safety valve body in the valve housing in a simple and reliable manner together with a low installation space requirement.
The safety valve body can be arranged in the interior of the valve piston. As a result, it is further possible to reduce the installation space required for the pressure-limiting valve.
It can also be provided that the safety valve body has a safety valve body sealing ring by which the pneumatic passage can be closed in a sealing manner in a closed position of the safety valve body.
Furthermore, it is possible that the safety valve body has a separate safety valve body spring which sets the safety valve body against the pneumatic passage in an open position of the safety valve body.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.